We report a case of severe poisoning in a 57-day-old infant who presented with vomiting, convulsions, and shock after ingesting a bottle of milk containing a decoction of Rhododendron simsii (紅杜鵑). The grandmother collected this toxic plant from a cultivated area, believing it was good for the airways. Grayanotoxin was detected in both the urine and plant specimens. The infant made a good recovery after requiring ventilatory support for 2 days. Rhododendron is a common gardening shrub in Hong Kong. Some Rhododendron species are poisonous and contain grayanotoxin. Intentional or accidental ingestion of toxic plants can be severe or even life-threatening. It is therefore essential that clinicians be familiar with local toxic plant species.